Technical advantages and regulatory compliance rules make it desirable to limit the amount of signal radiation that extends in a particular direction from an antenna system. For example, in some scenarios, the signal radiation in a particular direction must be controlled to meet regulatory requirements or to mitigate interference with other systems. Indeed, the Federal Communications Commission (FCC) limits the effective isotropic radiated power (EIRP) radiated in a conical region of +/−60° around the zenith (i.e. a skyward direction) to 21 dbm for a WiFi antenna operating in the 5 GHz U-NII 1 band, meaning that, for a radio with a maximum output power of 0.5 W (27 dBm), the maximum antenna gain in the skyward direction is less than −6 dBi. However, antenna gain outside of such the skyward direction, that is, in a primary region of interest, must be maintained with a specific gain requirement for a good RF communication signal. Indeed, the WiFi antenna operating in the 5 GHz band may have a peak gain requirement of 6 dBi for a good communication link. Accordingly, there are conflicting requirements, and such conflicting requirements are poorly addressed by known systems and methods. For example, known systems and methods to limit the amount of signal radiation in a particular direction include reducing the antenna system's overall gain, modifying the antenna system's radiation pattern, and modifying the antenna system's antenna beam width. However, each of these systems and methods includes disadvantages.
For example, systems and methods that reduce the overall gain of the antenna system detune the antenna system, add an attenuator, or reduce output power of a power amplifier. However, such adjustments lower the signal strength from the antenna system in all directions rather than in just an unwanted direction and, in addition to reducing the signal strength of a signal transmitted by the antenna system, may even reduce the signal strength of a signal the antenna system can receive. Furthermore, systems and methods that modify the antenna system's radiation pattern do so by adding a mechanical or electrical beam tilt to shift a main lobe of radiation away from the unwanted direction where low levels of signal radiation are desired. However, when the antenna system includes the mechanical down tilt, the antenna system must be mounted on a fixed or adjustable platform that is tilted so that a main antenna beam points away from the unwanted direction, thereby adding large and potentially complex mechanical structures to implement, which are dependent on an operator for correct installation. When the antenna system includes the electrical down tilt, a progressive phase shift is implemented to individual antenna elements of an antenna array, shifting a main lobe of radiation away from the unwanted direction, but limiting range because, at larger phase shifts, side lobes start to emerge and increase the signal radiation emitted in the unwanted direction. Further still, systems and methods that modify the antenna system's beam width do so by adding additional antenna elements to the antenna system, such as reflectors or directors, or increase a number of the antenna elements in the antenna array. However, these additional elements require additional volume and may increase peak gain, thereby exceeding FCC limits.
In view of the above, there is a continuing, ongoing need for systems and methods that can reduce radiation in an unwanted direction while simultaneously preserving signal radiation outside of the unwanted direction.